This invention relates generally to marine propulsion devices such as stern drive units and outboard motors including a shifting mechanism and a reversing transmission for coupling the motor to the propeller. In particular, the invention disclosed herein is an electronic system for reducing engine speed to facilitate shifting the transmission.
For the sake of background, several U.S. patents which disclose marine propulsion devices having reversing transmissions and shifting mechanisms are U.S. Pat. Nos. 3,842,788; 3,183,880; 3,977,356; 3,386,546; 3,919,510; and 3,858,101.
Attention is also invited to pending U.S. patent application Ser. No. 890,499, now U.S. Pat. No. 4,231,316, which is assigned to the assignee of this application. The cited application discloses a mechanism for effecting shifting of a transmission. It also disclosed an electronic circuit for interrupting engine ignition periodically to thereby reduce engine speed during a shifting operation to ensure positive engagement of a driving element with a driven element during the shifting or propeller reversing operation. In the prior application, resistance to shifting, which is a concomitant of improper transmission engagement, is sensed. An electronic circuit responds to shifting resistance by going through a definite timing sequence which results in ignition being killed periodically to thereby lower engine speed sufficiently for the transmission elements to properly engage. A possible problem with the system is that it becomes committed to go through a particular ignition-killing sequence without accounting for all of the engine operating characteristic variables in which case there can be overkill and, hence, stalling of the motor.